Glass compositions which exhibit the Faraday rotation phenomenon (in which plane polarized light which is transmitted through the glass is rotated due to the magnetic properties of the glass) are well known to those skilled in the art. Some of these compositions are described in, e.g., M. J. Weber's "Faraday Rotator Materials" (Lawrence Livermore Laboratory, Livermore, Calif., 1982).
For many applications, it is desirable that glass compositions which exhibit the Faraday rotation effect be transparent in both the visible and the infrared region of the light spectra. Thus, for example, many optical switches, modulators, and laser isolators could be constructed with a glass composition which is both transparent and which exhibits the Faraday effect in the infrared region of the spectrum. Unfortunately, a glass composition is not presently available which exhibits a strong Faraday effect (high Verdet coefficient) and is transparent beyond 4-5 microns.
It is an object of this invention to provide a glass composition which exhibits the Faraday rotation effect and which is substantially transparent over the entire spectrum from 400 to 6,000 nanometers.
It is another object of this invention to provide a glass composition which is more resistant to attack by water, base, and/or acid than prior art glass compositions and which has a relatively high transmittance in the infrared region of the light spectrum.
It is yet another object of this invention to provide a durable glass composition, suitable for optical switching applications, which has a transmittance greater than about 70 percent over the range of from about 400 to about 6,000 nanometers and which, in addition, does not show a substantial change in this transmittance over time even after being exposed to moisture.